- Email: [email protected]
Making a material difference in energy
ARTICLE IN PRESS Energy Policy 36 (2008) 4302–4309
Contents lists available at ScienceDirect
Energy Policy journal homepage: www.elsevier.com/locate/enpol
Making a material difference in energy$, $$ David Driver ,1 Materials UK—Energy Materials Group
a r t i c l e in f o
a b s t r a c t
Available online 23 October 2008
The extraction of fuels and their conversion into power requires an extensive range of materials. Energy reserves are increasingly found deep underwater or far below the ground, and in severe locations. The containment and use of energy resources imposes further constraints on structural materials, from the subzero conditions of liquefied gas containers to the containment of gas plasmas at several thousand degrees in fusion reactors. Structural materials have been developed to meet many of these requirements, but cheaper and longer-lasting alternatives are needed. As intermittent distributed power becomes more common, new materials are needed for fuel cells, combined heat and power, wind and wave power, and energy storage. As well as offering higher efficiency, new materials will cut the cost of energy generation and storage. Fuel-efficient transport and low-energy electrical equipment will also call for new materials, as will renewable energy and the ‘hydrogen economy’. The possible reinvigoration of nuclear power and the development of fusion will also pose continuing challenges for materials science. Energy materials priorities are identified for each of these important technology areas. & 2008 Queen’s Printer and Controller of HMSO. Published by Elsevier Ltd. All rights reserved.
Keywords: Energy conservation Turbine materials Fuel cells
1. Materials priorities for energy 1. Materials for energy conservation The Energy White Paper (EWP) states that ‘the cheapest, cleanest and safest way to meet emission targets is to use less energy’. Many of those energy savings will be achieved through the use of ‘smart’ functional materials and lowenergy materials processing. Specific examples are given later. Energy conservation is the No. 1 materials priority. By 2050 most energy consuming equipment will be monitored and controlled with minimum human intervention.
$ While the Government Office for Science commissioned this review, the views are those of the author(s), are independent of Government, and do not constitute Government policy. $$ Since this brief review was produced Materials UK (Mat.UK) has expanded the discussion in a series of Materials UK Energy Review 2007 documents:
Report Report Report Report Report
1: 2: 3: 4: 5:
Energy materials: strategic research agenda Fossil-fuelled power generation Nuclear energy materials Alternative energy technologies Energy transmission, distribution and storage
The reports are available via www.matuk.co.uk/energy.htm. Tel.: +44 1509 843391. E-mail address: [email protected] 1 Home Address: 33 West End, Long Whatton, Loughborough, Leicestershire LE12.5DW, UK.
2. Materials for turbine technology There is strong materials synergy across high-temperature turbine technology in areas such as condition monitoring, durability and extended component lifetimes. Competitive advantage can be obtained from transferable materials solutions. Information on high-integrity structural materials was dispersed during electricity and nuclear divestment. That valuable information should be collected and disseminated within the UK Energy community. The Materials Foresight Energy Group should act as facilitator and focus for UK and international collaboration. By 2050 UK experience on structural materials for turbine technology should be widely exploited within the UK and in developing nations, such as China and India, which hold a quarter of current coal reserves. Turbine technology for lower temperature wind and wave applications is considered later, together with materials for energy storage of such distributed intermittent power. 3. Materials for fuel cell technology [and hydrogen storage] Fuel cells offer independent means of generating electricity in a low-carbon economy and can be incorporated into gasification plant to increase efficiency. New electrode and membrane materials are needed for more efficient power generation with solid-state hydrogen storage providing a safe means of handling the new fuel. This third priority complements energy conservation and clean coal. 4. Functional materials for energy generation and conservation Functional/smart materials offer opportunities for direct energy conversion [e.g. photovoltaic solar panels] or
0301-4215/$ - see front matter & 2008 Queen’s Printer and Controller of HMSO. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.enpol.2008.09.061
ARTICLE IN PRESS D. Driver / Energy Policy 36 (2008) 4302–4309
energy-saving devices [e.g. light-emitting diodes (LEDs) and liquid crystal displays]. They supplement but do not supplant earlier technology. By 2050 ‘smart’ functional materials will be used in buildings, transport and equipment to sense, monitor and control power requirements for domestic and industrial needs. Such materials were discovered 50 years ago. In another 50 years they will be all pervasive and very sophisticated. Current multi-billion dollar silicon wafer processing technology may be replaced by alternative lower cost coating technology. New nanostructured materials may provide the base from which the functional revolution can take place. 5. Nuclear fission and fusion materials The nuclear sector is already designing fusion and Generation IV fission reactors. Materials development for these structures illustrates the way to the future: By 2050 there will be sufficient understanding of materials properties and long-term degradation mechanisms to allow computer-based analysis and prediction of behaviour from an atomic level to full engineering structures. Computing power will allow a range of design options to be considered, built, tested and operated in a virtual environment. Full validation is needed but virtual design and manufacture will allow several design iterations before an optimum structure is chosen. New processing routes for structural materials are likely to include near-net-shape manufacture whereby material and component are built up together. It is wasteful of material, time and energy, to produce bulk commodity products from which intricate shapes are then machined. Coatings and particle processing [e.g. laser deposition] will be manufacturing routes of the future. 6. New material options for energy Although much future structural materials development will be incremental, there are potential ‘step change/ disruptive materials’ that may transform the future. Nanostructures are such a family. Carbon nanotubes are only a few nanometres in diameter [50,000 times smaller than the width of a human hair] yet they are the world’s strongest known material. They can be incorporated into such diverse materials as concrete and polymer composites to significantly increase strength. They can also be joined together to form functional/semiconductor devices for solar cells and can act as membranes for filtering CO2 emissions. It would be fitting if this new carbon-based material could provide the basis for a next-generation low-carbon economy. Considerable material development is, however, needed to overcome expensive processing routes and health and safety issues.
not energy efficient. Composite body structures (Fig. 1) can halve current fuel consumption. They should be more widely used. Practical vehicles powered by fuel cell technology are expected by 2010. A major issue is storage of hydrogen fuel [see later]. For safety reasons, metal hydrides are favoured. A hydride tank is about 3 times larger and 4 times heavier than a petrol tank with the same fuel energy. This weight disadvantage will affect fuel consumption, even though emissions are environmentally friendly!
2.3. Green light on energy saving
The US has calculated that switching its 100 M traffic lights
from incandescent bulbs to LEDs (Fig. 2) would save $190 Mp/a and reduce energy consumption by 3 billion KW/h. This is equivalent to eliminating emissions from 443,000 cars each year [http://optics.org]. UK could make similar savings from LED lighting [traffic lights, warning signs, floodlighting, etc.] In the energy-efficient world of 2050, most lighting will use LEDs. Materials development will further improve efficiency. Future success depends on effective product champions and a responsible approach by all to energy conservation.
2.4. TV viewing
Individuals might choose energy-saving technology if better informed. A 55 in. plasma TV costs nearly $150 p/a in energy
Fig. 1. General Motors ultra-lite composite vehicle [www.scaled.com]
2. Priority 1—conservation/optimised energy use 2.1. Energy White Paper 2003: [EWP, Para 1.10/18 and 1.40]
‘‘To reduce CO2 emissions by some 60% from current levels by 2050’’.
2.2. Lightweight structural materials for transportation
Transport accounts for 35% of total UK energy consumption [EWP Chart 1.5]. Lightweight structures could greatly reduce that figure. Transporting a 0.1-ton human being in a 1.5-ton car is
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Fig. 2. Colour-specific light-emitting diodes.
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compared with o$15 p/a for current smaller liquid crystal display (LCD) sets. [http://reviews.cnet.com]. Large plasma screens consume as much power as an average freezer. Freezers have an energy rating. TVs do not. LCD technology is also suitable for larger screens. In October 2004, 40–45 in. LCD TVs became widely available. In March 2005, Samsung announced an 82 in. panel [http://www.samsung.com]. These large LCDs are much more energy efficient than plasma screens. Materials development continues. By 2050 such low-energy equipment will be common place. Flexible polymers may have become the visual medium with semiconductor pixels ink-jet printed onto the surface. This
technology is now being developed; it would allow moving images on flexible display screens that could be hung on walls or even worn in clothing! The future is bright thanks to innovative materials technology.
2.5. Power to the people Average UK housing stock has a life expectancy of well over 100 years. Installing best energy practice on all new buildings would not significantly influence energy consumption for several
Fig. 3. Plasma screen (L) and LCD (R) televisions.
Fig. 4. Coal-fired steam turbine power station.
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bladed turbine discs/rings or even structural ceramic materials. These options (and others) are being explored on aeroengine gas turbines and could be transferred to power turbines. Demonstration plant is needed to test both the operating economics and the long-term effectiveness/structural integrity of new systems. Europe and US programmes have been introduced to build zero-emission coal-fired power plant incorporating fuel cell technology to produce hydrogen and electricity with carbon capture and storage to remove CO2. They should be extended for other fuel options [oil gas, waste].
Fig. 5. A solid oxide fuel cell (SOFC) stack [www.ikts.fraunhoffer.de].
3.2.1. High-temperature power generation materials Developments are required in:
New alloys for ultra-supercritical conditions. Alloy development specifically for industrial gas turbines to decades. Retrofitted energy-saving technology to mature properties is needed. ‘Smart’ structures that identify and reduce wasteful energy usage, glass with controllable thermal transmittance, and power management devices for optimised operation are available. There are many materials options for energy conservation that should be more widely used (Figs. 3–5).
3. Priority 2—turbine technology
3.1. Energy White Paper 2003
‘‘Coal fired power generation helps widen diversity of the energy mix, provided ways can be found y to reduce carbon emissions. We will ysupport research to develop y cleaner coal technologies and carbon capture/storage’’ [EWP, Para 1.25]. Continued use of fossil fuels in electricity generation will require the use of carbon capture and storage (CCS) to severely restrict CO2. DTI has developed a Carbon Abatement Technologies (CAT) Strategy [DTI/Pub. URN 05/844] in which there are a range of material challenges. These include new high-temperature oxidation/corrosion-resistant materials to meet the changed combustion environments from oxy-combustion or the need to separate CO2 and hydrogen from gasification using functional separation membranes [also see below]. The CAT Strategy highlights biomass co-firing, which will lead to more aggressive boiler environments [e.g. superheater corrosion]. Gasification offers a near-term route to hydrogen generation and to the future use of chemical feedstocks for power.
improve alloy stability, corrosion resistance and reduce costs through higher yields. Advanced manufacturing methods and joining techniques to reduce costs and offer greater structural integrity. High strength rotor discs with improved processing, NDT and life prediction Advanced alloys and [ceramic] composites specifically for power generation Ceramic and metallic hot gas filters for clean gasification and combustion. Metallic membrane development for CO2 separation in coalfired plant.
Carbon nanotubes are being developed for membrane applications. Nanostructure filters with over a trillion microscopic pores per square inch allow gases and liquids to flow rapidly but block larger molecules. Such filters have potential application in desalination plant and for removing CO2 from emissions.
3.2.2. Coatings technology Coating technology has been identified as a critical area for future materials development and includes thermal/corrosion barriers for protection of combustion components in biomass and waste-to-energy. Nano- and smart coatings that respond to their environment are examples of coating trends. Many coating compositions can be applied today. Further developments are anticipated.
3.2. Key material science advances
The Clean Coal Technology Review of October 2002 [Status
Report 18—Advanced Materials for Power Generation] has called for an integrated R&D programme in 3 priority areas—high-temperature materials, protective systems and modelling. The latest turbines use ultra-supercritical steam at up to 700 1C/375 bar for high thermal efficiency. Structural steels are being developed via European collaboration while Japan is pursuing an independent materials programme. Continued materials R&D is needed to reduce emissions [SOx, NOx and CO2] Feasible materials solutions are possible in the short term for SOx and NOx. Carbon dioxide isolation (sequestration) requires longer-term R&D. While improved high-temperature turbine materials will be available by 2050 there is further scope for ambitious new high-temperature blade/coating combinations and for less bulky integrally
3.2.3. Computer modelling By 2050, materials development and structural design options for zero-emissions will be undertaken by computer modelling. UK has considerable experience in this area. That knowledge should be used to competitive advantage.
3.2.4. Oil, gas, biomass and waste incineration Materials issues for oil, gas, biomass and waste are similar to coal technology. Gas mixtures are, however, more complex and corrosion attack is more severe. Emissions control is needed, particularly for undifferentiated waste, but economics preclude sophisticated treatments. Specific material options are available for particular fuels. The choice is between new alloys for high corrosion resistance or ‘like-for-like’ replacement with low-cost materials. Currently the tendency is for cheap replacement.
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[e.g. carbon nanotubes] and membranes. Material development will provide more cost-effective and power-efficient devices that operate over a wider range of operating temperatures.
4. Priority 3—fuel cell technology 4.1. Fuel cell types
Portable hydrogen-powered proton exchange membrane
or polymer electrolyte membrane fuel cells (PEMFC) have potential for use in cars and power packs [e.g. cameras, mobile phones]. Water management, CO2 poisoning, cooling, and hydrogen storage are operational issues. Material options are discussed below. Direct methanol fuel cells (DMFC) use methanol, rather than hydrogen to feed the fuel cell. Storage of liquid methanol is easier than gaseous hydrogen and energy density is also orders of magnitude greater. Efficiency is, however, low and methanol is poisonous. Oxidation at the catalytic layer produces unwanted CO2. The cell also requires the presence of water, which limits energy density. Solid oxide fuel cells (SOFC) are intended mainly for combined heat and power (CHP) for domestic and industrial use. They currently operate at high temperatures (up to 1000 1C) but lower temperature (600 1C) versions are being developed, which will allow use of metallic components with better mechanical properties and thermal conductivity than the solid oxide electrolyte. SOFC operate on a wide range of fuels but require long start-up times (typically 8 h.). Newer [microtubular] designs promise faster start-up. Cost reduction is critical.
4.2. Key materials science advances
Durable membranes and improved catalysts are needed for
lower temperature cells. Solid oxide fuel cells (SOFC) require ceramics with improved thermal and mechanical stability. Durability depends on application. Portable battery pack fuel cells require 3-year lifetimes, whereas motor vehicles need 5–10 years. Power station fuel cells require lives up to 20 years. Component sintering conditions, membrane failure, corrosion, fuel contaminants, etc. all limit material durability. By 2050, materials development will enable the fuel cell market to use less expensive electrode materials [than platinum/palladium] and highly efficient gas flow materials
5. Hydrogen storage 5.1. Energy White Paper 2003 ‘‘The aim is to reduce CO2 emissions by 60% by 2050. This target is best met by increased use of hydrogen fuel.’’ [EWP, Para 1.10/1.18] 5.2. Current status
Hydrogen storage is important for long-term exploitation of
fuel cells. In the short term, hydrogen will be extracted from hydrocarbon fuels using steam reforming, combined with CO2 sequestration. Containment/transport of the gases is difficult Liquefied hydrogen containers and high-pressure gas cylinders will initially be used for hydrogen storage but solid-state hydrogen storage would be preferable. Materials options for all types of containment are being developed.
5.3. Key material science advances Solid-state hydrogen storage is possible using metal hydrides and carbon nanostructures (Fig. 6). Both options are being investigated as part of the UK EPSRC SUPERGEN Initiative. Hydride systems tend to be too bulky and heavy for efficient storage [see lightweighting], while nanostructures have health and safety issues
6. Renewables 6.1. Energy White Paper 2003 ‘‘Government recognises that specific measures are requiredy to achieve the target of supplying 10% of UK electricity from renewable energy by 2010’’ [EWP, Para 1.21].
Fig. 6. Structure of carbon C564 ‘buckeyball’ and nanotube.
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Fig. 7. Assembly of solar-powered photovoltaic cells.
Any major shift in primary fuel sources will require consider
able investment in hardware and extensive R&D [particularly for alternative fuels]. A major challenge facing the materials community is the sheer diversity of renewable energy sources and consequent material implications. Because of this diversity, materials R&D tends to be fragmented. Greater focus is needed.
7.3. Key material science advances
A range of functional materials are being developed. These
7. Solar energy—photovoltaics (PVs)
The Sun generates nearly a trillion, trillion kW of power2 and has done so at virtually the same rate for over 3 billon years.
In half an hour, enough of the Sun’s energy reaches the Earth’s surface to meet the World’s energy demand for a year [www.ecocentre.org.uk/solar-electricity].
devices will always provide secondary power in the UK because of unreliable weather, but the EWP is correct in its assertion that solar PV offers considerable potential for step change breakthroughs. Examples include: J dye-sensitised photochemical cells [e.g. nanocrystalline titanium dioxide]; J quantum dot solar cells [CdSe semiconductor absorbers in polymer/C60 composite]. This ‘buckyball’ structure has potential for low-cost, largearea fabrication. J Nanostructured oxide polymer composites. J Thin film inorganics—CdTe, GaAs, polycrystalline silicon. J Supercapacitors based on nanostructured materials. J Ultra-thin, anti-reflective and electrical conducting coatings. By 2050 several of these materials should have achieved production status.
To waste that energy seems careless! 7.1. Energy White Paper 2003
8. Wind power (Fig. 8)
Solar PV and wave/tidal power are areas in which increased investment is likely to lead to step change breakthroughs.’’ [EWP 2003, Para 4.15]
8.1. Key materials science advances
Polymer composite wind turbines are relatively lightweight
7.2. Current material status Solar cells with large-area single-crystal wafers (Fig. 7) are efficient but expensive. Polycrystalline/ribbon silicon is cheaper to produce but has reduced efficiency. Durable, low-cost/highefficiency PV materials and processes are being developed. 2
4 1023 kW, http://ircamera.as.arizona.edu/.
and corrosion-resistant making them ideal in hostile and inaccessible locations. Sensors incorporated into the structures during manufacture could enable service loads and damage accumulation to be monitored. The aim is to ‘fit and forget’ such devices. Energy storage and transmission remain critical issues. By 2050 composite structures could exhibit the following characteristics: J Appreciably higher strength. Carbon nanotubes added to polymer composites can increase stiffness and strength
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tenfold but contamination and health and safety issues remain. Cost-effective production routes are also needed. J Composite structures designed to respond to aerodynamic forces [aeroelastic tailoring] and changing shape [morphing] to optimise performance. Materials developments that address energy storage and transmission issues include: J Superconducting cables J Supercapacitors based on nanostructured materials for short-term storage J Batteries with near-instantaneous charging and highcapacity discharge [e.g. Toshiba lithium capacitors reported in 2005] J Insulation and phase change materials for heat stores.
9.2. Current materials status Materials exist for water turbines and wave power. Because of salt-corrosion and heavy seas, designers tend to over-engineer wave devices with resulting performance penalties. Corrosion, erosion and cavitation remain material issues. 9.3. Key material science advances
Existing materials need optimising for wave technology, with
more robust design criteria and improved life prediction methods. Composite materials offer higher corrosion resistance and condition monitoring [as for wind power]. Materials knowledge for water turbines may be transferable from marine technology. Most relevant materials technology is already available.
9. Water power (Fig. 9) 9.1. Energy White Paper 2003 10. Nuclear fusion and advanced nuclear fission ‘‘Solar PV & wave/tidal power are areas in which increased investment is likely to lead to step change breakthroughs’’. [EWP, Para 4.15]
10.1. Energy White Paper 2003: [EWP, Para 1.24 and 1.38]
‘‘Nuclear power is an important source of carbon-free
electricity. Current economics make it unattractive [and] there are important issues of nuclear waste’’. ‘‘Strong backing is given for international development of fusion power’’.
10.2. Nuclear fission 10.2.1. Key material science advances
Power generation structures use bcc steels with ‘low-activity’
Fig. 8. Composite wind turbines.
alloying additions. Previous typical materials issues have been environmentally induced cracking, thermal fatigue and ageing; loss of toughness caused by irradiation, wear, etc. Condition monitoring for such degradation mechanisms would be valuable.
Fig. 9. Wave power machines [top L: Pelamis; bottom L: LIMPET].
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Fig. 10. Split image of JET tokamak fusion reactor [hot plasma on right].
Alternative encapsulants to borosilicate glass are being
investigated for plutonium waste. Because of extended lifetimes, materials R&D and waste management rely heavily on computer modelling. Charged particle beams are used to approximate neutron irradiation for model validation purposes. Risk-management and non-destructive evaluation (NDE) are also considered at the design stage. Generation IV reactor designs are being evaluated and may enter service beyond 2030. Specialist steels will be needed for exotic Generation IV coolants [e.g. liquid sodium, lead].
10.3. Nuclear fusion Nuclear fusion is a long-term candidate for future power generation beyond 2050. Fusion is achievable only at very high temperatures [e.g. the Sun is a fusion reactor]. 10.3.1. Key material science advances
The hot gases of the fusion reaction are confined within a strong electrostatic or magnetic field. Materials science is
released from the task of developing a containment material but the issue of a plasma-facing material remains (Fig. 10). Graphite erodes rapidly. If tungsten is chosen, impurities can impair the plasma. Beryllium is currently the favoured containment material but health and safety issues remain. Compared with hot plasma containment, the material developments for hot gas transfer and turbine power components seem relatively straightforward! Large flux levels of highenergy neutrons [100 times more than in pressurised water reactors (PWR)] make structures radioactive. Low activation alloys [e.g. vanadium] with half-lives of tens, rather than thousands of years [as for fissile materials] make this problem less serious. Complex new alloy compositions are, however, still needed. There are some strong synergies between fusion and Generation IV fission materials. Both will use similar candidate materials [bcc and oxide-dispersion-strengthened steels] and operate under conditions that require high temperature, long life alloys capable of withstanding neutron bombardment. Both use similar theoretical modelling and neutron source experimental validation, for optimised alloy design and share similar damage-driven mechanisms [i.e. creation of defects and transmutant gases]. A materials testing facility is planned to evaluate fusion materials. This is currently at the design stage.
Contents lists available at ScienceDirect
Energy Policy journal homepage: www.elsevier.com/locate/enpol
Making a material difference in energy$, $$ David Driver ,1 Materials UK—Energy Materials Group
a r t i c l e in f o
a b s t r a c t
Available online 23 October 2008
The extraction of fuels and their conversion into power requires an extensive range of materials. Energy reserves are increasingly found deep underwater or far below the ground, and in severe locations. The containment and use of energy resources imposes further constraints on structural materials, from the subzero conditions of liquefied gas containers to the containment of gas plasmas at several thousand degrees in fusion reactors. Structural materials have been developed to meet many of these requirements, but cheaper and longer-lasting alternatives are needed. As intermittent distributed power becomes more common, new materials are needed for fuel cells, combined heat and power, wind and wave power, and energy storage. As well as offering higher efficiency, new materials will cut the cost of energy generation and storage. Fuel-efficient transport and low-energy electrical equipment will also call for new materials, as will renewable energy and the ‘hydrogen economy’. The possible reinvigoration of nuclear power and the development of fusion will also pose continuing challenges for materials science. Energy materials priorities are identified for each of these important technology areas. & 2008 Queen’s Printer and Controller of HMSO. Published by Elsevier Ltd. All rights reserved.
Keywords: Energy conservation Turbine materials Fuel cells
1. Materials priorities for energy 1. Materials for energy conservation The Energy White Paper (EWP) states that ‘the cheapest, cleanest and safest way to meet emission targets is to use less energy’. Many of those energy savings will be achieved through the use of ‘smart’ functional materials and lowenergy materials processing. Specific examples are given later. Energy conservation is the No. 1 materials priority. By 2050 most energy consuming equipment will be monitored and controlled with minimum human intervention.
$ While the Government Office for Science commissioned this review, the views are those of the author(s), are independent of Government, and do not constitute Government policy. $$ Since this brief review was produced Materials UK (Mat.UK) has expanded the discussion in a series of Materials UK Energy Review 2007 documents:
Report Report Report Report Report
1: 2: 3: 4: 5:
Energy materials: strategic research agenda Fossil-fuelled power generation Nuclear energy materials Alternative energy technologies Energy transmission, distribution and storage
The reports are available via www.matuk.co.uk/energy.htm. Tel.: +44 1509 843391. E-mail address: [email protected] 1 Home Address: 33 West End, Long Whatton, Loughborough, Leicestershire LE12.5DW, UK.
2. Materials for turbine technology There is strong materials synergy across high-temperature turbine technology in areas such as condition monitoring, durability and extended component lifetimes. Competitive advantage can be obtained from transferable materials solutions. Information on high-integrity structural materials was dispersed during electricity and nuclear divestment. That valuable information should be collected and disseminated within the UK Energy community. The Materials Foresight Energy Group should act as facilitator and focus for UK and international collaboration. By 2050 UK experience on structural materials for turbine technology should be widely exploited within the UK and in developing nations, such as China and India, which hold a quarter of current coal reserves. Turbine technology for lower temperature wind and wave applications is considered later, together with materials for energy storage of such distributed intermittent power. 3. Materials for fuel cell technology [and hydrogen storage] Fuel cells offer independent means of generating electricity in a low-carbon economy and can be incorporated into gasification plant to increase efficiency. New electrode and membrane materials are needed for more efficient power generation with solid-state hydrogen storage providing a safe means of handling the new fuel. This third priority complements energy conservation and clean coal. 4. Functional materials for energy generation and conservation Functional/smart materials offer opportunities for direct energy conversion [e.g. photovoltaic solar panels] or
0301-4215/$ - see front matter & 2008 Queen’s Printer and Controller of HMSO. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.enpol.2008.09.061
ARTICLE IN PRESS D. Driver / Energy Policy 36 (2008) 4302–4309
energy-saving devices [e.g. light-emitting diodes (LEDs) and liquid crystal displays]. They supplement but do not supplant earlier technology. By 2050 ‘smart’ functional materials will be used in buildings, transport and equipment to sense, monitor and control power requirements for domestic and industrial needs. Such materials were discovered 50 years ago. In another 50 years they will be all pervasive and very sophisticated. Current multi-billion dollar silicon wafer processing technology may be replaced by alternative lower cost coating technology. New nanostructured materials may provide the base from which the functional revolution can take place. 5. Nuclear fission and fusion materials The nuclear sector is already designing fusion and Generation IV fission reactors. Materials development for these structures illustrates the way to the future: By 2050 there will be sufficient understanding of materials properties and long-term degradation mechanisms to allow computer-based analysis and prediction of behaviour from an atomic level to full engineering structures. Computing power will allow a range of design options to be considered, built, tested and operated in a virtual environment. Full validation is needed but virtual design and manufacture will allow several design iterations before an optimum structure is chosen. New processing routes for structural materials are likely to include near-net-shape manufacture whereby material and component are built up together. It is wasteful of material, time and energy, to produce bulk commodity products from which intricate shapes are then machined. Coatings and particle processing [e.g. laser deposition] will be manufacturing routes of the future. 6. New material options for energy Although much future structural materials development will be incremental, there are potential ‘step change/ disruptive materials’ that may transform the future. Nanostructures are such a family. Carbon nanotubes are only a few nanometres in diameter [50,000 times smaller than the width of a human hair] yet they are the world’s strongest known material. They can be incorporated into such diverse materials as concrete and polymer composites to significantly increase strength. They can also be joined together to form functional/semiconductor devices for solar cells and can act as membranes for filtering CO2 emissions. It would be fitting if this new carbon-based material could provide the basis for a next-generation low-carbon economy. Considerable material development is, however, needed to overcome expensive processing routes and health and safety issues.
not energy efficient. Composite body structures (Fig. 1) can halve current fuel consumption. They should be more widely used. Practical vehicles powered by fuel cell technology are expected by 2010. A major issue is storage of hydrogen fuel [see later]. For safety reasons, metal hydrides are favoured. A hydride tank is about 3 times larger and 4 times heavier than a petrol tank with the same fuel energy. This weight disadvantage will affect fuel consumption, even though emissions are environmentally friendly!
2.3. Green light on energy saving
The US has calculated that switching its 100 M traffic lights
from incandescent bulbs to LEDs (Fig. 2) would save $190 Mp/a and reduce energy consumption by 3 billion KW/h. This is equivalent to eliminating emissions from 443,000 cars each year [http://optics.org]. UK could make similar savings from LED lighting [traffic lights, warning signs, floodlighting, etc.] In the energy-efficient world of 2050, most lighting will use LEDs. Materials development will further improve efficiency. Future success depends on effective product champions and a responsible approach by all to energy conservation.
2.4. TV viewing
Individuals might choose energy-saving technology if better informed. A 55 in. plasma TV costs nearly $150 p/a in energy
Fig. 1. General Motors ultra-lite composite vehicle [www.scaled.com]
2. Priority 1—conservation/optimised energy use 2.1. Energy White Paper 2003: [EWP, Para 1.10/18 and 1.40]
‘‘To reduce CO2 emissions by some 60% from current levels by 2050’’.
2.2. Lightweight structural materials for transportation
Transport accounts for 35% of total UK energy consumption [EWP Chart 1.5]. Lightweight structures could greatly reduce that figure. Transporting a 0.1-ton human being in a 1.5-ton car is
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Fig. 2. Colour-specific light-emitting diodes.
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compared with o$15 p/a for current smaller liquid crystal display (LCD) sets. [http://reviews.cnet.com]. Large plasma screens consume as much power as an average freezer. Freezers have an energy rating. TVs do not. LCD technology is also suitable for larger screens. In October 2004, 40–45 in. LCD TVs became widely available. In March 2005, Samsung announced an 82 in. panel [http://www.samsung.com]. These large LCDs are much more energy efficient than plasma screens. Materials development continues. By 2050 such low-energy equipment will be common place. Flexible polymers may have become the visual medium with semiconductor pixels ink-jet printed onto the surface. This
technology is now being developed; it would allow moving images on flexible display screens that could be hung on walls or even worn in clothing! The future is bright thanks to innovative materials technology.
2.5. Power to the people Average UK housing stock has a life expectancy of well over 100 years. Installing best energy practice on all new buildings would not significantly influence energy consumption for several
Fig. 3. Plasma screen (L) and LCD (R) televisions.
Fig. 4. Coal-fired steam turbine power station.
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bladed turbine discs/rings or even structural ceramic materials. These options (and others) are being explored on aeroengine gas turbines and could be transferred to power turbines. Demonstration plant is needed to test both the operating economics and the long-term effectiveness/structural integrity of new systems. Europe and US programmes have been introduced to build zero-emission coal-fired power plant incorporating fuel cell technology to produce hydrogen and electricity with carbon capture and storage to remove CO2. They should be extended for other fuel options [oil gas, waste].
Fig. 5. A solid oxide fuel cell (SOFC) stack [www.ikts.fraunhoffer.de].
3.2.1. High-temperature power generation materials Developments are required in:
New alloys for ultra-supercritical conditions. Alloy development specifically for industrial gas turbines to decades. Retrofitted energy-saving technology to mature properties is needed. ‘Smart’ structures that identify and reduce wasteful energy usage, glass with controllable thermal transmittance, and power management devices for optimised operation are available. There are many materials options for energy conservation that should be more widely used (Figs. 3–5).
3. Priority 2—turbine technology
3.1. Energy White Paper 2003
‘‘Coal fired power generation helps widen diversity of the energy mix, provided ways can be found y to reduce carbon emissions. We will ysupport research to develop y cleaner coal technologies and carbon capture/storage’’ [EWP, Para 1.25]. Continued use of fossil fuels in electricity generation will require the use of carbon capture and storage (CCS) to severely restrict CO2. DTI has developed a Carbon Abatement Technologies (CAT) Strategy [DTI/Pub. URN 05/844] in which there are a range of material challenges. These include new high-temperature oxidation/corrosion-resistant materials to meet the changed combustion environments from oxy-combustion or the need to separate CO2 and hydrogen from gasification using functional separation membranes [also see below]. The CAT Strategy highlights biomass co-firing, which will lead to more aggressive boiler environments [e.g. superheater corrosion]. Gasification offers a near-term route to hydrogen generation and to the future use of chemical feedstocks for power.
improve alloy stability, corrosion resistance and reduce costs through higher yields. Advanced manufacturing methods and joining techniques to reduce costs and offer greater structural integrity. High strength rotor discs with improved processing, NDT and life prediction Advanced alloys and [ceramic] composites specifically for power generation Ceramic and metallic hot gas filters for clean gasification and combustion. Metallic membrane development for CO2 separation in coalfired plant.
Carbon nanotubes are being developed for membrane applications. Nanostructure filters with over a trillion microscopic pores per square inch allow gases and liquids to flow rapidly but block larger molecules. Such filters have potential application in desalination plant and for removing CO2 from emissions.
3.2.2. Coatings technology Coating technology has been identified as a critical area for future materials development and includes thermal/corrosion barriers for protection of combustion components in biomass and waste-to-energy. Nano- and smart coatings that respond to their environment are examples of coating trends. Many coating compositions can be applied today. Further developments are anticipated.
3.2. Key material science advances
The Clean Coal Technology Review of October 2002 [Status
Report 18—Advanced Materials for Power Generation] has called for an integrated R&D programme in 3 priority areas—high-temperature materials, protective systems and modelling. The latest turbines use ultra-supercritical steam at up to 700 1C/375 bar for high thermal efficiency. Structural steels are being developed via European collaboration while Japan is pursuing an independent materials programme. Continued materials R&D is needed to reduce emissions [SOx, NOx and CO2] Feasible materials solutions are possible in the short term for SOx and NOx. Carbon dioxide isolation (sequestration) requires longer-term R&D. While improved high-temperature turbine materials will be available by 2050 there is further scope for ambitious new high-temperature blade/coating combinations and for less bulky integrally
3.2.3. Computer modelling By 2050, materials development and structural design options for zero-emissions will be undertaken by computer modelling. UK has considerable experience in this area. That knowledge should be used to competitive advantage.
3.2.4. Oil, gas, biomass and waste incineration Materials issues for oil, gas, biomass and waste are similar to coal technology. Gas mixtures are, however, more complex and corrosion attack is more severe. Emissions control is needed, particularly for undifferentiated waste, but economics preclude sophisticated treatments. Specific material options are available for particular fuels. The choice is between new alloys for high corrosion resistance or ‘like-for-like’ replacement with low-cost materials. Currently the tendency is for cheap replacement.
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[e.g. carbon nanotubes] and membranes. Material development will provide more cost-effective and power-efficient devices that operate over a wider range of operating temperatures.
4. Priority 3—fuel cell technology 4.1. Fuel cell types
Portable hydrogen-powered proton exchange membrane
or polymer electrolyte membrane fuel cells (PEMFC) have potential for use in cars and power packs [e.g. cameras, mobile phones]. Water management, CO2 poisoning, cooling, and hydrogen storage are operational issues. Material options are discussed below. Direct methanol fuel cells (DMFC) use methanol, rather than hydrogen to feed the fuel cell. Storage of liquid methanol is easier than gaseous hydrogen and energy density is also orders of magnitude greater. Efficiency is, however, low and methanol is poisonous. Oxidation at the catalytic layer produces unwanted CO2. The cell also requires the presence of water, which limits energy density. Solid oxide fuel cells (SOFC) are intended mainly for combined heat and power (CHP) for domestic and industrial use. They currently operate at high temperatures (up to 1000 1C) but lower temperature (600 1C) versions are being developed, which will allow use of metallic components with better mechanical properties and thermal conductivity than the solid oxide electrolyte. SOFC operate on a wide range of fuels but require long start-up times (typically 8 h.). Newer [microtubular] designs promise faster start-up. Cost reduction is critical.
4.2. Key materials science advances
Durable membranes and improved catalysts are needed for
lower temperature cells. Solid oxide fuel cells (SOFC) require ceramics with improved thermal and mechanical stability. Durability depends on application. Portable battery pack fuel cells require 3-year lifetimes, whereas motor vehicles need 5–10 years. Power station fuel cells require lives up to 20 years. Component sintering conditions, membrane failure, corrosion, fuel contaminants, etc. all limit material durability. By 2050, materials development will enable the fuel cell market to use less expensive electrode materials [than platinum/palladium] and highly efficient gas flow materials
5. Hydrogen storage 5.1. Energy White Paper 2003 ‘‘The aim is to reduce CO2 emissions by 60% by 2050. This target is best met by increased use of hydrogen fuel.’’ [EWP, Para 1.10/1.18] 5.2. Current status
Hydrogen storage is important for long-term exploitation of
fuel cells. In the short term, hydrogen will be extracted from hydrocarbon fuels using steam reforming, combined with CO2 sequestration. Containment/transport of the gases is difficult Liquefied hydrogen containers and high-pressure gas cylinders will initially be used for hydrogen storage but solid-state hydrogen storage would be preferable. Materials options for all types of containment are being developed.
5.3. Key material science advances Solid-state hydrogen storage is possible using metal hydrides and carbon nanostructures (Fig. 6). Both options are being investigated as part of the UK EPSRC SUPERGEN Initiative. Hydride systems tend to be too bulky and heavy for efficient storage [see lightweighting], while nanostructures have health and safety issues
6. Renewables 6.1. Energy White Paper 2003 ‘‘Government recognises that specific measures are requiredy to achieve the target of supplying 10% of UK electricity from renewable energy by 2010’’ [EWP, Para 1.21].
Fig. 6. Structure of carbon C564 ‘buckeyball’ and nanotube.
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Fig. 7. Assembly of solar-powered photovoltaic cells.
Any major shift in primary fuel sources will require consider
able investment in hardware and extensive R&D [particularly for alternative fuels]. A major challenge facing the materials community is the sheer diversity of renewable energy sources and consequent material implications. Because of this diversity, materials R&D tends to be fragmented. Greater focus is needed.
7.3. Key material science advances
A range of functional materials are being developed. These
7. Solar energy—photovoltaics (PVs)
The Sun generates nearly a trillion, trillion kW of power2 and has done so at virtually the same rate for over 3 billon years.
In half an hour, enough of the Sun’s energy reaches the Earth’s surface to meet the World’s energy demand for a year [www.ecocentre.org.uk/solar-electricity].
devices will always provide secondary power in the UK because of unreliable weather, but the EWP is correct in its assertion that solar PV offers considerable potential for step change breakthroughs. Examples include: J dye-sensitised photochemical cells [e.g. nanocrystalline titanium dioxide]; J quantum dot solar cells [CdSe semiconductor absorbers in polymer/C60 composite]. This ‘buckyball’ structure has potential for low-cost, largearea fabrication. J Nanostructured oxide polymer composites. J Thin film inorganics—CdTe, GaAs, polycrystalline silicon. J Supercapacitors based on nanostructured materials. J Ultra-thin, anti-reflective and electrical conducting coatings. By 2050 several of these materials should have achieved production status.
To waste that energy seems careless! 7.1. Energy White Paper 2003
8. Wind power (Fig. 8)
Solar PV and wave/tidal power are areas in which increased investment is likely to lead to step change breakthroughs.’’ [EWP 2003, Para 4.15]
8.1. Key materials science advances
Polymer composite wind turbines are relatively lightweight
7.2. Current material status Solar cells with large-area single-crystal wafers (Fig. 7) are efficient but expensive. Polycrystalline/ribbon silicon is cheaper to produce but has reduced efficiency. Durable, low-cost/highefficiency PV materials and processes are being developed. 2
4 1023 kW, http://ircamera.as.arizona.edu/.
and corrosion-resistant making them ideal in hostile and inaccessible locations. Sensors incorporated into the structures during manufacture could enable service loads and damage accumulation to be monitored. The aim is to ‘fit and forget’ such devices. Energy storage and transmission remain critical issues. By 2050 composite structures could exhibit the following characteristics: J Appreciably higher strength. Carbon nanotubes added to polymer composites can increase stiffness and strength
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tenfold but contamination and health and safety issues remain. Cost-effective production routes are also needed. J Composite structures designed to respond to aerodynamic forces [aeroelastic tailoring] and changing shape [morphing] to optimise performance. Materials developments that address energy storage and transmission issues include: J Superconducting cables J Supercapacitors based on nanostructured materials for short-term storage J Batteries with near-instantaneous charging and highcapacity discharge [e.g. Toshiba lithium capacitors reported in 2005] J Insulation and phase change materials for heat stores.
9.2. Current materials status Materials exist for water turbines and wave power. Because of salt-corrosion and heavy seas, designers tend to over-engineer wave devices with resulting performance penalties. Corrosion, erosion and cavitation remain material issues. 9.3. Key material science advances
Existing materials need optimising for wave technology, with
more robust design criteria and improved life prediction methods. Composite materials offer higher corrosion resistance and condition monitoring [as for wind power]. Materials knowledge for water turbines may be transferable from marine technology. Most relevant materials technology is already available.
9. Water power (Fig. 9) 9.1. Energy White Paper 2003 10. Nuclear fusion and advanced nuclear fission ‘‘Solar PV & wave/tidal power are areas in which increased investment is likely to lead to step change breakthroughs’’. [EWP, Para 4.15]
10.1. Energy White Paper 2003: [EWP, Para 1.24 and 1.38]
‘‘Nuclear power is an important source of carbon-free
electricity. Current economics make it unattractive [and] there are important issues of nuclear waste’’. ‘‘Strong backing is given for international development of fusion power’’.
10.2. Nuclear fission 10.2.1. Key material science advances
Power generation structures use bcc steels with ‘low-activity’
Fig. 8. Composite wind turbines.
alloying additions. Previous typical materials issues have been environmentally induced cracking, thermal fatigue and ageing; loss of toughness caused by irradiation, wear, etc. Condition monitoring for such degradation mechanisms would be valuable.
Fig. 9. Wave power machines [top L: Pelamis; bottom L: LIMPET].
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Fig. 10. Split image of JET tokamak fusion reactor [hot plasma on right].
Alternative encapsulants to borosilicate glass are being
investigated for plutonium waste. Because of extended lifetimes, materials R&D and waste management rely heavily on computer modelling. Charged particle beams are used to approximate neutron irradiation for model validation purposes. Risk-management and non-destructive evaluation (NDE) are also considered at the design stage. Generation IV reactor designs are being evaluated and may enter service beyond 2030. Specialist steels will be needed for exotic Generation IV coolants [e.g. liquid sodium, lead].
10.3. Nuclear fusion Nuclear fusion is a long-term candidate for future power generation beyond 2050. Fusion is achievable only at very high temperatures [e.g. the Sun is a fusion reactor]. 10.3.1. Key material science advances
The hot gases of the fusion reaction are confined within a strong electrostatic or magnetic field. Materials science is
released from the task of developing a containment material but the issue of a plasma-facing material remains (Fig. 10). Graphite erodes rapidly. If tungsten is chosen, impurities can impair the plasma. Beryllium is currently the favoured containment material but health and safety issues remain. Compared with hot plasma containment, the material developments for hot gas transfer and turbine power components seem relatively straightforward! Large flux levels of highenergy neutrons [100 times more than in pressurised water reactors (PWR)] make structures radioactive. Low activation alloys [e.g. vanadium] with half-lives of tens, rather than thousands of years [as for fissile materials] make this problem less serious. Complex new alloy compositions are, however, still needed. There are some strong synergies between fusion and Generation IV fission materials. Both will use similar candidate materials [bcc and oxide-dispersion-strengthened steels] and operate under conditions that require high temperature, long life alloys capable of withstanding neutron bombardment. Both use similar theoretical modelling and neutron source experimental validation, for optimised alloy design and share similar damage-driven mechanisms [i.e. creation of defects and transmutant gases]. A materials testing facility is planned to evaluate fusion materials. This is currently at the design stage.